#pragma warning(disable:4996)
#include<stdio.h>
int main()
{
	size_t n;
	int count = 1;
	double sum, flag;
	sum = 0.0, flag = 1.0;
	scanf("%d", &n);
	for (size_t i = 1; i <= n; i++) {
		sum += flag*i / count;
		count += 2;
		flag = -flag;
	}
	printf("%.2lf", sum);
	return 0;
}